Resonantly driven power toothbrush having a pressure-sensing capability using a hall effect sensor

Abstract

The toothbrush includes a handle portion which includes a power drive system ( 14 ) and further includes a brushhead assembly ( 20 ), which includes a brushhead arm having a brush element ( 21 ) at a distal end thereof A drive train assembly ( 12 ) is responsive to a drive signal from the power assembly for converting the action of the power assembly to a motion of the brushhead assembly. A magnet ( 30 ) is secured to the rear of the drive train, with a Hall effect sensor ( 32 ) mounted within the magnetic field produced by the magnet as the toothbrush moves in operation. Pressure on the brush element produces a phase shift of the Hall sensor output. A processor ( 15 ) determines the value of the phase shift of the Hall sensor signal as pressure is applied to the brush member and produces a signal indicative of the pressure applied by using stored information ( 71 ) which relates phase shift to pressure for the particular appliance.

What is claimed is: 
     
       1. A power toothbrush, comprising:
 a handle portion containing a power system; 
 a brushhead assembly, including a brush member having a bristle field at a distal end thereof; 
 a drive train assembly responsive to a drive signal of the power system and configured to produce a motion of the brushhead assembly; 
 a magnet secured to the drive train and positioned to move in conjunction with the brushhead assembly motion, the magnet producing a magnetic field; 
 a Hall effect sensor mounted within the handle portion and positioned adjacent the magnet, wherein the Hall effect sensor is configured to detect a change in phase between the drive signal of the power system and the motion of the brushhead assembly as pressure on the bristle field changes as applied to teeth of a user during operation under load conditions; and wherein the Hall effect sensor is further configured to respond with a phase shift in a Hall effect sensor output signal relative to the phase of the drive signal; and 
 a microprocessor control configured to determine a value of the phase shift of the Hall effect sensor output due to pressure on the bristle field during brushing operations and further configured to produce a feedback signal indicative of said pressure by using stored information in the power toothbrush relating values of phase shift pressure. 
 
     
     
       2. The power toothbrush of  claim 1 , wherein the processor is calibrated such that the Hall effect sensor output signal is coincident in phase with the drive signal under no-load conditions. 
     
     
       3. The power toothbrush of  claim 1 , including a zero crossing circuit for determining the phase shift. 
     
     
       4. The power toothbrush of  claim 1 , wherein the microprocessor control includes the capability of averaging the signal output of the Hall effect sensor over several cycles and for filtering noise from the Hall effect sensor signal output. 
     
     
       5. The power toothbrush of  claim 1 , wherein the microprocessor control uses the stored information to correlate the output of the Hall effect sensor with a first pre-established threshold and to provide feedback information to the user when pressure on the brush member exceeds the first threshold value. 
     
     
       6. The power toothbrush of  claim 5 , wherein the first threshold value represents a maximum pressure value. 
     
     
       7. The power toothbrush of  claim 5 , including a second pre-established threshold representing a minimum pressure value. 
     
     
       8. The power toothbrush of  claim 1 , wherein the output signal from the Hall effect sensor is continuous and the feedback signal from the microprocessor is also continuous, representing a continuous indication of pressure on the brush member. 
     
     
       9. The power toothbrush of  claim 1 , wherein the feedback information is in a form recognizable by the user. 
     
     
       10. The power toothbrush of  claim 1 , wherein the phase shift under load conditions is determined through quadrature sampling.